FIELD OF THE INVENTION AND RELATED ART STATEMENT
1. FIELD OF THE INVENTION
[0001] The present invention relates generally to an image display apparatus, and more particularly
to an image display apparatus having plural linear cathodes wherefrom multi-electron
beams are emitted and are deflected by electrostatic vertical deflection electrodes.
2. DESCRIPTION OF THE RELATED ART
[0002] The above-mentioned image display apparatus in the prior art is shown in FIG. 7 and
FIG. 8.
[0003] Linear cathodes 1 are disposed parallelly to each other in one end portion of a vacuum
enclosure 10 as shown in FIG. 7. A repeller 25 for reflecting electrons emitted from
the linear cathodes 1 are disposed between the linear cathodes 1 and a back end of
the vacuum enclosure 10. A fluorescent screen 5 is disposed in the opposite end portion
of the vacuum enclosure 10. The fluorescent screen 5 has an anode 6 on its inside
surface. An electron beam extraction electrode 2, which is a planer metal plate and
has a number of apertures 8 lined up in plural rows, each disposed in front of and
adjacent to the linear cathode 1, is provided between the linear cathode 1 and the
fluorescent screen 5. Vertical deflection electrodes 13 and 14 are formed by, for
example, metalizing process on surfaces of substrates 30 made of insulation material,
and are disposed between the fluorescent screen 5 and the electron beam extraction
electrodes 2, in a manner parallel to the linear cathode 1 and perpendicuclar to the
electron beam extraction electrode 2. The electron beams 4, ... emitted from the cathode
1 pass the apertures 8, and travel between the vertical deflection electrodes 13 and
14, and finally reach to the fluorescent screen 5. The electron beams 4, ... are deflected
by an electrostatic field which is formed by the vertical deflection electrodes 13
and 14, which is formed by the deflection voltage applied tnereto.
[0004] Horizontal deflection electrodes and acceleration electrodes are disposed between
the vertical deflection electrodes 13, 14 and the fluorescent screen 5 in a portion
shown by a chain line 20 in Fig. 8. However detailed construction is not shown in
the drawing because those constructions are not important to the present invention.
[0005] Theoretically, an image of a horizontal line on the fluorescent screen 5 made by
the electron beams 4, ... are expected to form a linear line. However, by some reasons
that the vertical deflection electrodes warp, there is voltage drop along the length
of the linear cathodes 1, ... the electron beams 4, ... are not uniformly deflected.
As a result, the images on the fluorescent screen 5 are distorted. Mechanical correction
of the warped vertical deflection electrodes are difficult, since the warp of the
vertical deflection electrodes is found after the assembly of components and subsequent
sealing off of the image display apparatus in the vacuum enclosure 10. Hence, a yield
rate in fabrication has been poor.
OBJECT AND SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide an image display apparatus wherein
a distortion of images which is formed on a fluorescent screen can be corrected by
variation of voltage to be applied to respective vertical deflection electrodes which
are divided into plural segments.
[0007] An image display apparatus in accordance with the present invention comprises:
linear cathodes for emitting electron beams,
an electron beam extraction electrode having apertures for extracting electron beams
and disposed parallelly to the linear cathodes,
a fluorescent screen disposed parallelly to the electron beam extraction electrode,
and
electrostatic deflection electrodes which is disposed between the electron beam extraction
electrode and the fluorescent screen, and each is divided into at least two pieces
of at least a piece disposed nearer to the electron beam extraction electrodes and
another piece disposed nearer to the fluorescent screen.
[0008] Electrostatic fields are formed by the divided vertical deflection electrodes are
formed by impressing different voltages to respective segments of the deflection electrodes.
Correction of the distorted images due to the distortion of the deflection electrodes
can be made for wide extent by selecting the division ratio and the voltage to be
applied to the respective segments of the vertical deflection electrodes.
BRIEF DESCRIPTION OF THE DRAWING
[0009]
FIG. 1 is a persepective view of an image display apparatus of an embodiment in accordance
with the present invention.
FIG. 2 is a cross-sectional view of the embodiment of FIG. 1.
FIG. 3(a), FIG. 3(b) and FIG. 3(c) are cross-sectional views for showing principle
of deflection of an electron beam.
FIG. 4 is a plane view of rectangular vertical deflection electrodes for showing principle
of the present invention.
FIG. 5(a) and FIG. 5(b) are plane views of vertical deflection electrodes embodying
the present invention.
FIG. 6(a) and FIG. 6(b) are illustration of images to be represented on a straight
line by the electron beams on a fluorescent screen 5.
FIG. 7 is the persepective view of the image display apparatus in the prior art.
FIG. 8 is the cross-sectional view of the image display apparatus of FIG. 7.
DESCRIPTION OF THE PREFEERED EMBODIMENT
[0010] An embodiment of an image display apparatus in accordance with the present invention
is shown in FIG. 1 and FIG. 2. Linear cathodes 1 are disposed in one end portion of
a vacuum enclosure 10 as shown in FIG. 2. Although two linear cathodes are shown in
FIG. 1 and FIG. 7, plural linear cathodes, for example 15--60, are used in the practical
image display apparatus in accordance with the present invention. A repeller 25 for
reflecting electrons emitted from the linear cathodes 1 is disposed between the linear
cathodes 1 and a back end of the vacuum enclosure 10. A fluorescent screen 5 is disposed
in the opposite end portion of a vacuum enclosure 10. The fluorescent screen 5 has
an anode 6 on its inside surface. An electron beam extraction electrode 2, which is
a planer metal plate and has a number of apertures 8 lined up in plural rows, each
disposed in-front of and adjacent to the linear cathode 1, is provided between the
linear cathode 1 and the fluorescent screen 5. Vertical deflection electrodes 3a,
3b, 3c and 3d are formed by, for example, metalizing process on surfaces of substrates
30 made of insulation material, and are disposed between the fluorescent screen 5
and the electron beam extraction electrode 2, in a manner parallel to the cathode
1 and perpendicular to the electron beam extraction electrode 2. A pair of vertical
'deflection electrodes 3a and 3c are disposed nearer to the electron extraction electrodes
2 on both sides of each electron beam path passing through the apertures 8. Another
pair of vertical deflection elec-\' trodes 3b and 3d are disposed nearer to the fluorescent
screen 5 on both sides of each electron beam path passing through the apertures 8.
The electron beams 4, ... from the cathode 1 pass the apertures 8, and travel between
the vertical deflection electrodes 3a, 3b and the vertical deflection electrodes 3c,
3d, and finally reach to the fluorescent screen 5. The electron beams 4, ... are deflected
by an electrostatic field which is formed by the vertical deflection electrodes 3a,
3b, 3c and 3d, which is formed by the deflection voltages applied across the linear
cathode 1 and the respective vertical deflection electrodes 3a, 3b, 3c and 3d. Four
power sources of different voltages for the vertical deflection electrodes 3a, 3b,
3c and 3d are provided (not shown in Fig. 1 and 2), so that respective vertical deflection
electrodes can be impressed with different voltages each other.
[0011] First, principle of the present invention is elucidated with reference to FIG. 3(a),
FIG. 3(b), FIG. 3(c) and FIG. 4.
[0012] The electrons emitted from the linear cathode 1 pass through the plural apertures
8 of the electron beam extraction electrode 2, and rows of electron beams 4, ... are
formed. When the electron beams come out of the apertures, at first, they are deflected
by an electric field formed by the vertical deflection electrode 3a and 3c. Subsequently,
the electron beams are deflected by an electric field formed by the vertical deflection
electrode 3b and 3d. For example, in case that rectangular vertical deflection electrodes
3a, 3c, 3b and 3d as shown in FIG. 4 are used, when a voltage applied to the vertical
deflection electrodes 3a is higher than that applied to the electrodes 3b, 3c and
3d, and the vertical deflection electrodes 3a and 3c are wider than the vertical deflection
electrode 3b and 3d as shown in FIG. 3(a), the electron beam 4 is widely deflected
as shown by large deflection valve y,. When the vertical deflection electrodes 3a,
3c, 3b and 3d have equall widths as shown in FIG. 3(b), the electron beam 4 is deflected
in a medium extent as shown by a medium deflection value y
z. When the vertical deflection electrodes 3b and 3d are wider than the vertical deflection
electrodes 3a and 3c, the electron beam 4 is deflected in a smallest extent as shown
by a small deflection valve Y
3.
[0013] Plane-views of vertical deflection electrodes of embodiments in accordance with the
present invention are shown in FIG. 5(a) and FIG. 5(b). The vertical deflection electrodes
3a and 3b are formed to concave and a convex shapes respectively, as shown in FIG.
5(a). In the embodiment, when a voltage applied to the vertical deflection electrode
3a is lower than that applied to the vertical deflection electrode 3b, the electron
beams which pass the central portion B of the vertical deflection electrode 3a and
3b are more deflected than the elec- . tron beams which pass the end portions A and
C.
[0014] When an image for a straight horizontal line produced by spots made by the electron
beams on the fluorescent screen 5 is not linear but is a curve as shown by black dots
27 in FIG. 6(a) due to inclination of the initial speeds of the electron beams along
the positions of the linear cathode, use of the vertical deflection electrodes 3a
and 3b as shown in FIG. 5(a) are recommendable. A deflection voltage (negative) which
is larger than that of the vertical deflection electrode 3a is applied to the vertical
deflection electrode 3b. Hence, the electron beams passing the central portion B of
the vertical deflection electrodes 3a and 3b are deflected more than those passing
the end portions A and B. As a result, the distortion from the straight line of the
images on the fluorescent screen 5 is corrected to straight line as shown by small
circles 26 in FIG. 6(a).
[0015] When an image for a straight horizontal line produced by spots made by the electron
beams on the fluorescent screen 5 inclines to the straight horizontal line as shown
by black dots 27 in FIG. 6-(b), use of the vertical deflection electrodes 3a and 3b
as shown in FIG. 5(b) are recommendable. A deflection voltage (negative) which is
larger than that of the vertical deflection electrode 3a is applied to the vertical
deflection electrode 3b. Hence, the electron beams passing the left portion D of the
vertical deflection electrodes 3a and 3b are deflected more than those passing the
right portion E. As a result, the distortion from the straight line of the images
on the fluorescent screen 5 is corrected to straight line as shown by small circles
26 in FIG. 6(b).
1. An image display apparatus comprising:
linear cathodes (1) for emitting electron beams,
an electron beam extraction electrode (2) having apertures (8) for extracting electron
beams and disposed parallelly to said linear cathodes (1),
a fluorescent screen (5) disposed parallelly to said electron beam extraction electrode
(2), and
electrostatic deflection electrodes (3a, 3b, 3c, 3d) which is disposed between said
electron beam extraction electrode (2) and said fluorescent screen (5), and each is
divided into at least two pieces of at least a piece disposed nearer to the electron
beam extraction electrode (2) and another piece disposed nearer to the fluorescent
screen(5).
2. An image display apparatus in accordance with claim 1, wherein
difference voltages are applied to said respective electostatic deflection electrodes
(3a, 3b, 3c, 3d).
3. An image display apparatus in accordance with claim 1, wherein
a shape of said electrostatic deflection electrode - (3a, 3b, 3c, 3d) is concave.
4. An image display apparatus in accordance with claim 1, wherein
a shape of said electrostatic deflection electrode - (3a, 3b, 3c, 3d) is convex.
5. An image display apparatus in accordance with claim 1, wherein said electrostatic
deflection electrodes (3a, 3b, 3c, 3d) have linearly changing widths from one end
to another end.